During the past year, clinical studies relating to the utilization of serum neuron specific enolase (NSE) levels in oat cell lung cancer and pediatric neuroblastoma patients have been carried further. We have now assessed large numbers of patients with each of these neuroendocrine neoplasms and shown that elevated serum NSE levels are of considerable diagnostic and prognostic value in both patient groups. We have also focused during the past year on the molecular biology of the brain enolases and have been successful in cloning the gene for both NSE and non-neuronal enolase (NNE). We have several cDNA probes for each of these human proteins. The amino acid sequence of human NSE has been determined as well as the degree of homology between NNE and NSE. Studies are currently in progress involving the chromosomal mapping of both the human NSE and NNE genes. In situ hybridization studies are also in progress using the cDNA probes with preliminary results showing that the NSE messenger RNA is highly localized in neurons. Developmental studies of the NNE to NSE switch in differentiating neurons using the cDNA probes are expected to provide key insights regarding neuron specific gene expression.